Jump to content

Putting off piston ring repair, for how long?


Recommended Posts

Hello,

(---Edited two days later, edit shown in ()'s. -- very sorry, embarrassed - reason: I took down measurements at first stroke then after max pressure, but I wrote below the first stroke.)

It has been a while since I posted.  One of my dear TR3A's troubles is low compression. I wrote about it here 2 years ago, listed my dry/wet readings and received excellent advice. But I have not had the engine pulled apart to fix it. 

-- Today, readings are a bit worse.  I generally measured 80 psi (,first stroke and max 110 psi) or so dry and 140 wet.

-- TR is very hard to start due to this low compression, and much harder to start in winter when pistons and rings shrink a bit due to the cold.

-- But, after about 5 minutes of crank for 6 seconds, wait for 30 seconds, and repeat, I finally get a slight kick-back feeling on engine and then it starts. I have to then spend 5 minutes of careful warmup with throttle and choke before it idles by itself and I can drive it. Afterwards, no smoke from exhaust, plenty of power. I am assuming that the heat of running acts to snug up the pistons and rings to the cylinder and allow engine to almost be normal. Afterwards, on the same day, a press of the starter switch gives instant starting.

My question is a dumb one since I know that my engine needs works.  So, I won't actually ask how long I can keep this up. Not many owners would. But I still can enjoy my TR anytime and turn those heads along the way.

Opie

Edited by Opie
wrong #
Link to post
Share on other sites

That’s a big compression increase just for oiling the bores, normally I’d expect maybe 15% say.


Hmmm are you a …gentle, ? or should we say considerate, ? enough of this shilly-shallying.
Are you encouraged to cruise gently at 50 mph ( “mind my hair,” coming from the passenger side,) or even “do you drive it like you stole it” which also doesn’t cut the mustard.

 If you havn’t been recommended already I should remove the spark plugs and squeeze piston ring “ freer” in there ( about 5cc a bore) and allow to soak into the rings to unstick them. If you don’t have any do the same with diesel which searches, lubricates and helps free stuck rings. The contamination to the engine is so minor no problems will arise even if it all hits the sump.

Then replace plugs and start the engine and drive to the bottom of a long steady gradient ( motorways are good for this) and give it some BMEP running ( Brake Mean Effective Pressure… Google it).

Drive at about 2500 revs in 4th gear and floor the throttle… and hold the throttle down into the carpet. When the revs get to 4500 revs throttle off and brake the speed of the car down again to 2500 revs and repeat. I do it between some local islands about 3 miles apart. The choice of top gear and flooring the throttle will try to expand the piston rings into the cylinder liner walls. This will help free off any stuck rings and bed the rings into the liner walls, removing any glaze caused by easy footing the car. I’d devote maybe 45 mins to this…and then next week do it again, an continue like this for a month. 
Then repeat your compression tests and see if it’s improved.

Mick Richards

Link to post
Share on other sites

Ahh the Italian Tune Up.    Works wonders on engines that have been gently used for years.   
 

 

In your part of the world think about Seafoam or Marvel Mystery oil to work the rings loose.

 

Link to post
Share on other sites

Just a thought. Poor compression can also be due to poor valve seats. Most likely would be exhaust valve which can get burnt out more quickly if not using hardened seats to compensate for lead free petrol.

I had the same symptoms as you, but went ahead with a major engine rebuild. But the main area that was defective was valve seats.

Engines have a remarkable ability to run once they are running even if they are very difficult to start.

Good luck.

Link to post
Share on other sites

 "Poor compression can also be due to poor valve seats"

Which when you add oil to the cylinder increases the compressions from 80 to 140 lbs   ! !......... I don't think that is likely. Poor starting which is just achieved after churning the engine for some while is indicative of incremental achieved compressions, first time 80 lbs second time 95 lbs 3rd time etc until you reach combustion mix, hence why I think it's stuck or not bedded in piston rings. 

Mick Richards

Link to post
Share on other sites

Edited my first post. Sorry.

I will take all new readings this next week and post them.

My report should have said 110 psi dry and 140 wet instead of 80/140.

Motorsport Mickey stated gently above that the original #'s were amiss. Good catch.

thanks.

Opie

Link to post
Share on other sites

Hi Opie, when doing the compressions wedge the pistons fully up in the carb, a piece of stiff cardboard edgeways on on top of the bridge does the trick.

Mick Richards

Link to post
Share on other sites

Mick,

Do you mean to prop the throttle fully open AND prop the carb piston fully open at same time when doing compression testing?

Link to post
Share on other sites
On 1/23/2022 at 3:06 PM, Opie said:

Mick,

Do you mean to prop the throttle fully open AND prop the carb piston fully open at same time when doing compression testing?

Yes, what you don't want are a partial reading on a cylinder caused by the churn and the pistons in the carb flapping about. Take out the imponderables and wedge the pistons up and then whatever the suck through the carbs it remains constant.

Mick Richards

Link to post
Share on other sites

Compressions should be tested with throttles wide open and no restrictions so get someone to hold the carb pistons up to be certain it is unrestricted.

Jumps in compression suggest a piston seal issue. At best just stuck in an engine that has stood but more likely wear. Unlucky if broken as that probably won't be greatly helped by a drop of oil. 

Valve seal issues won't be hugely be changed by a drop of oil. 

It's not an engine out job to re-ring or even swap the liners if badly worn.

Link to post
Share on other sites

As promised. I took new readings today, but nothing new it seems.  I will investigate a re-ring job as suggested above and try to determine if it is a job for the shop or one I could hope to accomplish at home.  My initial thought is that if I have to go to the shop, the cost will be high enough that I may as well go all the way and do pistons, rings, and liners.  But if I can do it in my garage I will just try the re-ring.image.png.ad1247568c635a75d4100439dd89ea95.png
on edit March 19, 2022. I just today noticed my attempt at pasting a spreadsheet got garbled. The dates should have been different over a 10 year period. Sorry. Another note: It took four tries to start.  Each try was for 3 seconds of starting try.  30 seconds between tries.  Started on 5th try.  About 5 minutes of nursing choke before it would idle normally.  Restart afterwards was first push starting, as it always has been.

I could go on like this forever I guess, but I will eventually surrender the TR to relatives or sell it as I am 74 now and 'forever' does not seem as long as it once did.  ha.  A new owner will not be as forgiving as I am and will expect a proper starting TR.

compression-testing-jan-2022d.pdf

Edited by Opie
wrong dates in table
Link to post
Share on other sites

Opie,

Is there some reason you won't consider using the rebedding in system I recommended ?

Apart from whatever jallop you wish to use to help free up piston rings running it on the road is free apart from a little enjoyable you and TR time ? seems a no brainer to me. Try rebedding the piston rings and if it then doesn't work pay a specialist to lift the head and refurb the engine.

Mick Richards

Link to post
Share on other sites

Mickey,

The reason I haven't tried your previous re-beddiing suggestion is that I have been cold and lazy.  I have nothing to lose, so I will try your method soon and post results!

Your suggestion above, after putting in the freeing oil is to: Drive at about 2500 revs in 4th gear and floor the throttle… and hold the throttle down into the carpet. When the revs get to 4500 revs throttle off and brake the speed of the car down again to 2500 revs and repeat. I do it between some local islands about 3 miles apart. The choice of top gear and flooring the throttle will try to expand the piston rings into the cylinder liner walls. This will help free off any stuck rings and bed the rings into the liner walls, removing any glaze caused by easy footing the car. I’d devote maybe 45 mins to this…and then next week do it again, an continue like this for a month. 
Then repeat your compression tests and see if it’s improved.

Someone calls this an Italian tune-up.  ha

Another reason is also that I read too much on-line.  Here is one worry I read today.  It refers to "over-rich" causing problems. I thought carefully about that and went to the TR3 and pushed in a small wire into the spark plug hole and scraped a bit of black residue from inside and put into my palm and rubbed it with my finger.  It definitely felt slightly gritty and therefore abrasive.  I have had many occasions of improper rich carb setting over the years and so I may have doomed my engine??

If an engine is allowed to idle in an overly-rich condition for as little as 30 minutes, this can cause sufficient cylinder wall damage where the wall may exhibit a dull, dark grey color. If this occurs, the engine will likely require complete disassembly and fresh honing.

https://www.enginebuildermag.com/2018/05/how-to-break-in-your-piston-rings-the-right-way/

Link to post
Share on other sites

Opie,

That’s referring to initial ring break in, your engine has run for some years and mileage.
Whatever condition your upper wall of the liners are it either will be improved with the BMEP running, or it won’t. There are dozens of owners ( me included ) that have run engines without the correct mixture when in use. 
Rich or weak, it doesn’t necessarily mean the end of the world and can’t be recovered. 
“the engine will likely require complete disassembly and fresh honing.” …it doesn’t say definitely.
As John Wayne says…get on your horse and ride, ! Try it for a month…and see.

Mick Richards

Edited by Motorsport Mickey
Link to post
Share on other sites

Mick, (and Peter W)

Just an update, so I can go back later to read this and see what's what.  Still not a good day to do the re-bedding. 

Reading the nice long current topic on this forum about fuel leaks and smell, there was a lot of carb tuning advice.  So, enthused, I removed the carb pistons, changed the carb piston oil to 20W, ran the mixture screw all the way up and then down 12 flats on each. Started the TR3 in 5 tries as before.  Made some minor mixture adjustments.  Got idle to 800.  Rev's nicely with only a slight lag.   All looking good except for the low compression and poor starting.   

So, I'll find a day to do the re-bedding and then write up the results.  

Peter W, do you recommend the Seafoam treatment before the re-bedding (Italian tune-up) or only if I see no improvement?  And while your recommended video above shows adding the Seafoam to the crankcase, do you also think I should spray a can into the intakes while idling?

Thanks.

Opie

Edited by Opie
Link to post
Share on other sites

Re the poor starting  Opie -  are you sure you are pulling the choke all the way out?   I had similar trouble until I realised that was the problem.  On the Tr3/3a with H6 carbs it can take a mighty pull, further than you think. The choke knob needs to come nearly 2 inches out from the dash, then magically the engine starts first or second try.  

Link to post
Share on other sites

Just a cautionary word Opie, rebedding the piston rings cannot be done if they are stuck in the piston grooves ! so it's necessary to use the Sea Foam before trying any remedial rebedding in of the rings. 

The rings need to be working in their normal manner for the engine to be able to force them out of their ring grooves and into the liner surface gouging (steady, we are talking microns) grooves down the walls. This removes the polished surfaces allowing cylinder excess oil to be scraped off into the sump whilst leaving enough oil for the piston not to seize.

The reference to an "Italian tune up" is slightly misleading. Italian cars many with their sporting pedigree Ferrari, Alfa, Fiat even are noted for being "screamers" with acceleration only being halted by the rev counter needle bending around the stop pin ! Commonly referred as such it summons up images of starting the car and planting the foot into the carpet screaming through all gears up to maximum revs...when in fact because of the excess revs in the wrong area of the torque band...that doesn't help you bed in the rings !

The engine needs to be fully loaded in it's highest Brake Mean Effective Pressure (Google it) area...which normally occurs well below max revs at around maximum torque ( 4 cylinder engines about 3500 revs !... doesn't conjure up images that suits an Italian tune up to me !   It is this BMEP which occurs upon the downward POWER stroke of the engine which pushes out the rings from the piston. Hence the advice to carry it out on long uphill road stretches where you can accelerate in 4th gear at FULL throttle (this extra effort loads the engine) between 2500 and up to 4500 revs continually. The effort issued through the engine to scrape through any polishing is gradual and may well take a month of continual BMEP use (as stated) before improvement can be measured... but it gets you out of the house and is more pleasurable than having to strip the engine with attendant costs ! 

Mick Richards

Edited by Motorsport Mickey
Link to post
Share on other sites

As Mick has written   Dose the upper cylinder area as directed to get the rings free, then do the BMEP improvement drive by loading the engine at midrange revs as Mick suggests.   

Link to post
Share on other sites

Rob,

I am looking at different items each day while planning my re-bedding procedure when it gets a bit warmer.

Today I want to consider your advice about the choke.  I want to know if my choke travel is sufficient to lower the jet enough to provide adequate fuel, as you mention above.  While measuring the choke switch travel in the dash, I do get the two inches you mention.  But can you or anyone tell me how far the jet should be lowered?  Maybe my linkage is faulty and jets are not lowering enough? As pictures show, my jet goes down about 3/8" upon full choke.  I researched the SU website but can not find a specification for jet travel during choking.

Let me know how far the jet should travel down, in your experience.  Of, course, I could remove the choke linkage and lower the jets farther, but I fear lowering them so much that the internal gland cork is passed and then raising the jet back up may be impossible.

thanks,

Opie

IMG_0754ssss.jpg

IMG_0753ssss.jpg

Link to post
Share on other sites

Rob, (regarding choke)

I kept looking and found one answer: from ( https://sucarb.co.uk/technical-carburetters-introduction 

"""Operation of the cold start mixture control (7) will lower the jet down the needle (maximum movement 7/16" or 11 mm) exposing a large annulus and so providing the rich mixtures required for the cold start and initial 'warm up' period."""

Since mine is 3/8", it needs a 1/16" more lowering.  I can't believe that will make much difference, but I will try, and also check fuel level inside jet to specifications: """The fuel level on an S.U. is not critical, and need not be treated with meticulous accuracy-the normal level is 3/8 in. under the rectangular inner facing known as the jet bridge, but this is rather difficult to observe even with the suction chamber and piston removed and the jet fully dropped."""

link here to SU website

ps - I know I am getting off the original topic about the rings, but the real initial reason I am looking at everything is that it is not the poor compression, it is the poor starting.  If I can get the TR3 to start easily even though I have poor compression, then I will rethink the whole matter and just enjoy the car.  Yes, a long shot, but here's my summary so far:

1. Poor starting - but car runs fine after starting.  Timing, carbs, spark all fine tuned.

2. Check compression, --- low

3. Predict bad rings or stuck rings.

4. Boroscope shows no cylinder damage and minimum wear, still having good cross-hatching marks.

5. Plan to re-bed the rings with Mickey's procedure on the highway soon. And use Seafoam to soak rings prior.

6. But, until I get on highway, I will try soon to increase choke function to see if TR starts easier than 5 tries when cold.  Even if this improves starting, I will still do the re-bedding.

Thanks,

Opie

jet lower21.png

Link to post
Share on other sites

11 to 12mm is what mine looks to do Opie - difficult to measure accurately with the car parked close to the garage wall !   

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.